Other Oil Engines. 709 is placed above j and is connected to it by two pipes (for oil and air). When the pressure in the two tanks becomes equal the oil runs into j by gravitation. Lubrication is effected in the usual manner, at all parts of the engine except the cylinder j the oil condensed within which is ample for the purpose. Several forms of oil engines are now made by other firms, but none spray the oil. In some, liquid oil is evaporated in a hot chamber, forming vapour and gas, which is mixed with air and fired as usual; and it is said no deposit occurs in ordinary working. In others, perfect oil-gas is produced, and then ex- ploded with air, but the engine must be often cleaned from tarry matter. (See Appendix II., p. 915 ; also p. 1165.) Oil Engines for Motor Cars.—The requirements of motor cars have developed an engine of very small weight using a light benzine oil called 'petrol.' Further information on these important engines will be found in Appendix 11.^ p. 915 ; Appendix IV., p. 963; and Appendix V.9 p. 999; also p. 1182. Trials of Boilers, Steam Engines, Gas Engines, and Oil Engines.—See Appendix I 11.,p. 937 et seq. Balancing of Engines.—See Appendix IL,p. 897, Appen- dix IV.) p. 967, and Appendix Ff., p* 1199. Hot-air Engines.—See Appendix //, p. 915. Steam Turbines.—See pp. 895, 966, and 1168.